Nanobubbles and the nanobubble bridging capillary force

• Published in: Advances in colloid and interface science 2010-02, Vol.154 (1), p.30-55
• Main Authors: Hampton, M.A., Nguyen, A.V.
• Format: Article
• Language: English
• Subjects: Atomic force microscopy; Capillary Action; Chemistry; Colloidal state and disperse state; Dissolved gas; Exact sciences and technology; General and physical chemistry; Hydrophobic and Hydrophilic Interactions; Microscopy, Atomic Force; Nanobubble bridging capillary force; Nanobubbles; Nanoparticles - chemistry; Surface physical chemistry; Surface Properties; Water
• ISSN: 0001-8686; 1873-3727
• DOI: 10.1016/j.cis.2010.01.006

Interactions between hydrophobic surfaces at nanometer separation distances in aqueous solutions are important in a number of biological and industrial processes. Force spectroscopy studies, most notably with the atomic force microscope and surface-force apparatus, have found the existence of a long range hydrophobic attractive force between hydrophobic surfaces in aqueous conditions that cannot be explained by classical colloidal science theories. Numerous mechanisms have been proposed for the hydrophobic force, but in many cases the force is an artifact due to the accumulation of submicroscopic bubbles at the liquid–hydrophobic solid interface, the so called nanobubbles. The coalescence of nanobubbles as hydrophobic surfaces approach forms a gaseous capillary bridge, and thus a capillary force. The existence of nanobubbles has been highly debated over the last 15 years. To date, experimental evidence is sound but a theoretical understanding is still lacking. It is the purpose of this review to bring together the many experimental results on nanobubbles and the resulting capillary force in order to clarify these phenomena. A review of pertinent nanobubble stability and formation theories is also presented.